Studies in our laboratory over the past 8 years have provided background for examining surface membranes from mammalian cells under a variety of conditions. The role of the surface membrane in various aspects of cellular behavior is being closely examined. More specifically, the chemical nature and metabolism of glycoproteins in surface membranes as these proteins relate to cell division, tumor development and other pathological states are under investigation. Differences have been found in the glycoproteins of the cell surface during cell division, after transformation by RNA or DNA viruses and in tumor cells. It is anticipated that the pursuit of these differences will (1) contribute to the molecular architecture of the cell surface; (2) show a direct relationship of these changes to the malignant or rapidly dividing cell; (3) open possibilities for immunotherapy of cancer; and (4) contribute to the definition of other pathological states where surface phenomena are indicated.